Adolph Hitler was never a German citizen, he was Austrian. Before WWI, this was the Austro-Hungarian Empire. He came into Germany by way of military service to Germany in WWI. Before Chamberlain's betrayal of Czechoslovakia, there was the Anschluss, the annexation of Austria to Germany by Adolph Hitler and the Nazis when they came to power. Nobody noticed and nobody cares about this history to this day.

Really, who annexed who?